package com.wc.alorithm_luogu._前缀和与差分.海底高铁;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.StringTokenizer;

/**
 * @Author congge
 * @Date 2025/1/10 8:57
 * @description
 * https://www.luogu.com.cn/problem/P3406
 */
public class Main {
    /**
     * 思路：
     * 计算最小费用, 我们得计算经过每个过路费多少次
     * 差分经过每个站的次数
     * 然后贪心计算最小值
     */
    static FastReader sc = new FastReader();
    static PrintWriter out = new PrintWriter(System.out);
    static int N = 100010;
    static int[] a = new int[N], b = new int[N], c = new int[N], p = new int[N];
    static long[] d = new long[N];
    static int n, m;

    public static void main(String[] args) {
        n = sc.nextInt();
        m = sc.nextInt();
        for (int i = 1; i <= m; i++) p[i] = sc.nextInt();
        for (int i = 1; i < n; i++) {
            a[i] = sc.nextInt();
            b[i] = sc.nextInt();
            c[i] = sc.nextInt();
        }

        for (int i = 1; i < m; i++) {
            int l = Math.min(p[i], p[i + 1]), r = Math.max(p[i], p[i + 1]) - 1;
            d[l] ++;
            d[r + 1] --;
        }

        for (int i = 1; i < n; i++) d[i] += d[i - 1];

        long res = 0;
        for (int i = 1; i < n; i++) {
            long buy = c[i] + b[i] * d[i];
            long nobuy = a[i] * d[i];
            res += Math.min(buy, nobuy);
        }
        out.println(res);
        out.flush();
    }
}

class FastReader {
    StringTokenizer st;
    BufferedReader br;

    FastReader() {
        br = new BufferedReader(new InputStreamReader(System.in));
    }

    String next() {
        while (st == null || !st.hasMoreElements()) {
            try {
                st = new StringTokenizer(br.readLine());
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return st.nextToken();
    }

    int nextInt() {
        return Integer.parseInt(next());
    }

    String nextLine() {
        String s = "";
        try {
            s = br.readLine();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return s;
    }

    long nextLong() {
        return Long.parseLong(next());
    }

    double nextDouble() {
        return Double.parseDouble(next());
    }

    // 是否由下一个
    boolean hasNext() {
        while (st == null || !st.hasMoreTokens()) {
            try {
                String line = br.readLine();
                if (line == null)
                    return false;
                st = new StringTokenizer(line);
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
        return true;
    }
}

